Jet lag is a syndrome of behavioral, cognitive, and physical symptoms that result when travelers are exposed to a sudden shift of the day-night cycle. These symptoms impact on alertness and performance of airline and military personnel and the safety of the traveling public. They may also exacerbate medical and psychiatric illness, and frequent flyers may face increased risk of disease. The long-term objective of this project is to develop a practical and effective treatment for jet lag using the Bio-Brite Light Visor to phase-shift circadian rhythms. Phase 1 demonstrated that the visor was effective in phase-shifting human circadian rhythms and accelerating circadian reentrainment following a westward flight across 6 time zones, but the effect on reentrainment rate was not sufficient to improve sleep, performance, or subjective measures of jet lag. Phase 2 is designed to improve the efficacy of the light treatment by implementing changes to the visor itself and to the light treatment schedule. These changes will be tested first in laboratory experiments, and then in a field study with both eastward and westward flights across 6 time zones (New York-Zurich-New York). Bright light (3000 lux) or dim red light (control) treatment will be scheduled for 3 h on the three mornings immediately preceding the eastward flight, and on the three evenings immediately following the westward flight. Subjects will also be required to avoid exposure to bright light at specific times after the eastward flight. Circadian reentrainment rates will be examined, using salivary dim light melatonin onset (DLMO) as phase reference. Other jet lag indices will include sleep quality and duration, determined from wrist actigraphic recordings and from scores on a subjective sleep quality questionnaire, performance on a psychomotor vigilance task, and subjective assessments of mood, daytime sleepiness, and other jet lag symptoms. Phase 2 will also include a data analysis component aimed at generating light exposure and avoidance schedules keyed to individual chronotype and to travel origin and destination.